The present technique relates generally to production of polyphenylene sulfide (PPS). In particular, the present technique relates to washing PPS with a base (e.g., sodium hydroxide) to reduce the amount of off-gassing during the subsequent melt processing of the PPS.
This section is intended to introduce the reader to various aspects of art which may be related to various aspects of the present techniques that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present techniques. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Polyphenylene sulfide (PPS), a member of a more general class of polymers known as poly(arylene) sulfide (PAS), is a high-performance engineering thermoplastic that may be heated and molded into desired shapes in a variety of manufacturing, commercial, and consumer applications. PPS may be used in the preparation of fibers, films, coatings, injection molding compounds, and fiber-reinforced composites, and is well-suited for demanding applications in appliance, automotive, and electrical/electronic industries. PPS may be incorporated as a manufacturing component either alone or in a blend with other materials, such as elastomeric materials, copolymers, resins, reinforcing agents, additives, other thermoplastics, and the like. Initially, PPS was promoted as a replacement for thermosetting materials, but has become a suitable molding material, especially with the addition of glass and carbon fibers, minerals, fillers, and so forth. In fact, PPS is one of the oldest high-performance injection molding plastics in the polymer industry, with non-filled grades commonly extruded as wire coatings.
PPS polymer is an attractive engineering plastic because, in part, it provides an excellent combination of properties. The molecular structure of PPS may readily form a thermally stable crystalline lattice, providing PPS with a semi-crystalline morphology and a high melting point, which may range from about 265° C. to about 315° C. Because of its molecular structure, PPS may char during combustion, making the material inherently flame resistant. Further, PPS is resistant to aggressive chemical environments, e.g., not dissolving in solvents of temperatures below about 200° C., and may become precision molded to tight tolerances. In summary, PPS is thermally stable, inherently non-flammable without flame retardant additives, and possesses excellent dielectric and insulating properties. Other properties include dimensional stability, high modulus, and creep resistance. The beneficial properties of PPS are due in part, to the stable chemical bonds of its molecular structure, which impart a relatively high degree of molecular stability (and therefore resistance) toward both thermal degradation and chemical reactivity.
Although the properties of PPS structures were known since the early 20th century, an industrially viable synthesis was only developed in the late 1960s. In 1967, Phillips Petroleum Company of Bartlesville, Okla. disclosed a method for producing PPS through the reaction of para-dichlorobenzene and sodium sulfide, as illustrated by the reaction below.

This condensation polymerization (or step polymerization) marked the beginning of industrial-scale commercialization of PPS. In 1972, Phillips Pertroleum Company began commercial-scale production of PPS, and this PPS was soon noted for having an effective balance of thermal and chemical resistances, nonflammability, and electrical insulating properties. Today, PPS is manufactured and sold under the trade name Ryton® PPS by Chevron Phillips Chemical Company LP of The Woodlands, Tex. Other sources of PPS include Ticona, Toray, and Dainippon Ink and Chemicals, Incorporated, among others.
PPS may be blended or compounded with various additives to provide desired properties. The PPS may be may be heated, melted, extruded, and molded into desired shapes and composites in a variety of processes, equipment, and operations. The PPS may be subjected to heat, compounding, injection molding, blow molding, precision molding, film-blowing, extrusion, and so forth, depending on the desired application.
However, off-gassing of PPS can be a problem during melt processing of the PPS resin. Such off-gassing has been observed to be more prevalent in, but not limited to, PPS produced wherein the polymerization step is terminated via flashing process solvent from the polymerization solution. A higher degree of off-gassing of PPS resins can lead to a number of undesirable processing complications, such as mold plate-out, melt bubbles, PPS product or defects, and so on. There exists a need for methods to produce lower off-gassing PPS. Presently, there exists a significant need for lower off-gassing flash resins in the marketplace.